The present invention relates to a protective casing with ring for shafts, in particular Cardan shafts.
The invention relates to protections, generally made of plastic material, destined to cover externally shaft portions and joints of transmission shafts, commonly cardanic shafts. Such protections normally comprise a soft casing, and an essentially rigid ring and tubular element. The casing covers the joint, whereas the tubular element covers the shaft portion. The ring, split longitudinally and destined to engage with a circumferential groove obtained on the inner fork of the joint, is used to maintain the casing in position, and possibly also the tubular element, allowing for the normal rotation of the joint. Commonly, to prevent the ring from detaching in use, a rigid cylindrical cap is provided to block the ring onto the circumferential groove of the joint fork, and the soft casing is inserted on the rigid cap, normally by snapping it in.
For reasons of cost-efficiency, practicality and functionality, single-piece casing and cap, made of a soft material, are already constructed. Prior art solutions however present a drawback, mentioned below. The ring and the tubular element are kept in position by a band, which is part of the single-piece casing and cap; as a result of stresses, and since said single piece, especially at high temperatures, is subject to warping, the ring, not being constrained any longer, risks widening and disengaging the tubular element and the joint casing. This not only could bring about a relative motion between tubular element and casing, but it also has obvious negative consequences for safety.
The above drawback has already been resolved in the case of small joints, with a soft casing blocking a ring and a tubular element. Inserting, from the shaft side, the casing on the ring, which is engaged on the circumferential groove of the joint fork, two tabs of the ring snap in corresponding seats obtained in the casing, preventing the inverse motion, and thus detachment. On disassembly, two holes provided on the casing in correspondence with the tabs of the ring allow to insert the tip of a tool, for instance a screwdriver, and to act on the tabs, bending them and disengaging them from the aforesaid seats of the casing.
In case of large joints, the problem of the stable connection of the ring and of the casing in all operating conditions cannot be resolved through the simple system mentioned above, because the casing is deformable. Moreover, the tabs of the ring, which are forced onto the seats of the casing as a result of high axial forces, tend to warp them and to disengage therefrom. It it not possible to construct multiple locking tabs, both due to construction problems and because disassembling the protection would require the simultaneous pressure on multiple ring tabs to bend them and disengage them from the casing.